This invention relates to a gauge for a machine tool. More specifically, this invention relates to a gauge for determining whether a conductive element of the machine tool, such as a cutting element, fence, gauge rod, gauge shaft, or guiding surface, is positioned at a predetermined angle with respect to a reference surface on the machine tool.
Machine tools typically have a conductive element, such as a cutting element, fence, gauge rod, gauge shaft, or guiding surface, supported in a predetermined orientation with respect to a reference surface over which a work piece is guided toward a cutting element. As just one specific example of such a machine tool, a table saw comprises a circular conductive saw blade supported at a predetermined angle with respect to a saw table. A work piece is guided over the saw table towards the saw blade so that the work piece is cut at an angle determined by the angle between the saw blade and the saw table. This angle can be any almost angle, but usually it is either 90.degree. or 45.degree. to the surface of the saw table.
The angle between the conductive element and the reference surface typically is adjustable to enable one to return the cutting element to the predetermined angle when it deviates from the predetermined angle or to provide different cutting angles on the work piece. There is a need, therefore, to be able to accurately adjust the angle of the conductive element with respect to the reference surface and to verify that the angle is adjusted to the desired value.
Various approaches have been suggested in the past to accurately set and verify the angle of conductive elements with respect to reference surfaces. One approach is a visual inspection procedure involving the use of a machinist's square having two straight edges connected together at a right angle, or at any angle to which it is desired to adjust the cutting element. One of the edges of the square is placed on the reference surface and the other edge is placed against the conductive element. The operator then visually inspects the conductive element to ascertain if it is parallel to edge of the square placed against the conductive element. If not, the operator then knows that the conductive element is not at the prescribed angle. The conductive element then can be adjusted so that it properly is parallel to the edge of the square. This procedure is unsatisfactory because debris tends to collect on the square, the square tends to become deformed in heavy use, and great visual acuity and concentration are required to ascertain to great accuracy whether the conductive element is parallel to the square along the entire edge of the square.
McNeece U.S. Pat. No. 3,724,084 refers to a probe element for checking the alignment of a tool with respect to a work piece. The probe element has a plurality of electrically conductive elements positioned in a stacked array and separated by non-conductive members, each conductive element connected in series with an indicator. When the tool is placed against the conductive elements, the tool completes a conductive circuit between each of the indicators and a power source through the structure supporting the tool and the indicators. When the tool is in proper alignment, all of the indicators are lit. This arrangement is costly because of the number of indicators and conductive circuits required. This arrangement also can only be used with tools supported by conductive structures.
Newton U.S. Pat. No. 4,383,369 refers to a device for adjusting the working edges of a moveable head on mill and shop tools. This device has a housing enclosing a battery and has a number of spaced electrical contacts so arranged that an electrical circuit is completed through an indicator when one of the contacts engages a fixed location site on the tool and the other contact engages the working edge of the tool. The circuit thus is completed through the support for the cutting element. This arrangement is unsatisfactory because a plurality of measurements must be taken in order to ascertain the alignment of the working edge. Like the apparatus of the McNeece patent above, the device of the Newton patent requires that it be used with cutting elements having conductive supports.
This invention overcomes the foregoing problems of the prior art by the provision of the simple gauge for ascertaining and verifying in one operation the angle made by a conductive element with respect to a reference surface over which a work piece is guided in a predetermined alignment with respect to a cutting tool. This invention relates to a gauge which can be used with a wide variety of machine tools, including those not having conductive reference surfaces, such as radial arm saws and routers, which typically have tables constructed of non-conductive materials, such as wood or wood by-products.